Since the curl_easy_setopt() call accepts several hundred different options
and the various options accept a variety of different types of arguments, it
is very important to read up on the specifics and provide exactly the argument
type the specific option supports and expects. Passing in the wrong type can
lead to unexpected side-effects or hard to understand hiccups.

The perhaps most important option that every transfer needs, is the URL.
libcurl cannot perform a transfer without knowing which URL it concerns so you
must tell it. The URL option name is as all options are prefixed
with and then the descriptive name—all using uppercase
letters. An example line setting the URL to get the ““ HTTP
contents could look like:

It is, of course, good form to check the return code to see that nothing went
wrong.

Since curl_easy_setopt() is a vararg function where the 3rd argument can use
different types depending on the situation, normal C language type conversion
cannot be done. So you must make sure that you truly pass a ‘long’ and not
an ‘int’ if the documentation tells you so. On architectures where they are
the same size, you may not get any problems but not all work like
that. Similarly, for options that accept a ‘curl_off_t’ type, it is
crucial that you pass in an argument using that type and no other.

Enforce a curl_off_t:

Get handle options

No, there’s no general method to extract the same information you previously
set with ! If you need to be able to extract the
information again that you set earlier, then we encourage you to keep track of
that data yourself in your application.